Gas Mileage FAQ - Page 18
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This is a discussion on Gas Mileage FAQ within the Everyday Impreza Talk forums, part of the Community - Meet other Enthusiasts category; Originally Posted by Ingo Do you know GENERATORS? I mean the ones at like hospitals. There is a very real ...

  1. #256
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    Quote Originally Posted by Ingo View Post
    Do you know GENERATORS? I mean the ones at like hospitals. There is a very real relation between electrical load and HP generated (used) and related fuel consumption.
    And the alternator is a REAL generator, even if it's not very large.
    Sure, draw does have an effect on rotational resistance. Is it even enough to mention when discussing MPG?

    I mean, you can power a whole concert off of a ****ty lawn mower generator...

    You're not even really running an audio system off the alternator, really. You're just using the alternator to charge the battery. I guess having an audio system might cause your battery to need to charge longer to remain full... I doubt you'd ever be able to measure an MPG difference unless you did a massive or second alternator upgrade.

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  3. #257
    Registered User Ingo's Avatar
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    Take it this way: The alternator has probably about 60Amp output. At 12V that's (12x60) 720 Watts. 700-some Watts equals 1 HP. That's the load and related fuel the alternator will take. Pretty simple, really. The rear defroster probably draws 15 Amps alone. Lights add up to maybe 120W (10Amps) Blowers, secondary air pump, fuel pump etc all draw off the electric system. The alternator supplies all of that until it reaches it's limits. If more is needed the battery delivers that until load goes down and then the alternator delivers it all AND charges the batt back up. It makes no difference if the alternator charges battery and battery supplies all of alternator supplies all including charging the batt. It all ends up the same. It's like having a waterline going into a bucket and having a faucet in the bottom of the bucket...
    A/C, power steering and so on only add to the additional loads in a straight mechanical way...
    You can't have everything - where would you put it?

  4. #258
    Registered User itiswhatitisnt's Avatar
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    Last Night, I average 30.6 MPG @ 65 MPH

    -Time: 11:05 PM/PST. Outside Temp: 68 Degrees.
    -Traveled 60 Miles to achieve 30.6 MPG.
    -Cruise Control was set @65 MPH
    -Stock Tune

  5. #259
    Registered User MountainView's Avatar
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    Quote Originally Posted by itiswhatitisnt View Post
    Last Night, I average 30.6 MPG @ 65 MPH

    -Time: 11:05 PM/PST. Outside Temp: 68 Degrees.
    -Traveled 60 Miles to achieve 30.6 MPG.
    -Cruise Control was set @65 MPH
    -Stock Tune
    Nice.

    I was close to that the other night, until I hit the smallest hills. People that live in flat areas certainly have an advantage here.

  6. #260
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    MPG update

    Thought I'd post an update since my last plot is nearly a year old. Two things happened about 10k miles ago. I moved into town (less highway driving) and my check engine light has been coming on and I've been experiencing rough idle.
    2011 wrx - stock

    Click image for larger version. 

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    edit: for clarity

  7. #261
    Registered User akaGONZO's Avatar
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    does getting an exhaust and/or cold air intake increase or decrease fuel efficiency assuming your driving practices remain the same?
    -akaGONZO

    "When the going gets weird, the weird turn pro." - Hunter S. Thompson

  8. #262
    UnBanned Sinister's Avatar
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    Quote Originally Posted by akaGONZO View Post
    does getting an exhaust and/or cold air intake increase or decrease fuel efficiency assuming your driving practices remain the same?
    Tricky question. Short side of it, if you drive conservatively now... You'll improve mileage. If you drive aggressively now... It'll get worse. Below are my explanations.


    Cold air intake brings in colder air, colder air means leaner condition which the ECU compensates for by injecting more fuel. (that's why we have an IAT bulb in the MAF housing).

    The cold air intake is less restrictive. That means less resistance, which means more power at lower RPMs with less throttle.

    So... With conservative habits, the mileage should be better. With aggressive habits, it should be worse.

    Less restrictive exhaust means more flow, more scavenging and therefore more volumetric efficiency. More efficiency means more gas mileage. But, it also means at higher throttle percentages, more air and fuel can be injected.
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  9. #263
    Registered User akaGONZO's Avatar
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    that's more or less what I thought ; your explanation makes it clearer. I want to get them but wanted the reality of what I was in for with regards to fuel consumption.
    -akaGONZO

    "When the going gets weird, the weird turn pro." - Hunter S. Thompson

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    Glad I helped a little
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  11. #265
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    I haven't read all of this thread but I average about 24 in the winter, and 26-27 in the summer. I used fuelly, and my numbers are all based on calculation, not the gauge in the car. My best mpg on a tank was 28.5. my average over 37K miles is 25.1 mpg. My average price per gallon over that time has been 3.60, making my car cost 14.8 cents per mile in fuel.
    2013 Subaru WRX named BlueRex
    2003 Jeep Rubicon, special zombie apocalypse edition

  12. #266
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    Thank you for the read. I have a 20hour drive with my subie soon!

  13. #267
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    According to my gauge, I managed to get 30.8 today on my 2015. This was a 34 mile drive and mostly highway, so yeah I was feathering the throttle quite a bit maintaining average speed around ~70mph

    Sent from my HTC One_M8 using Tapatalk

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    Regardin the WRX gas mileage, I have a 2014 sedan WRX (Past model) and I'm a little worried regarding the bad mpg that I'm having. I drive mostly in the city and I cannot have a better mpg than 17-17,5. More weird is that I don't drive like a crazy, standing on the gas pedal all the time, in fact, I drive more like a grandpa. I care all the time trying to have a good mpg, but I'm still having bad numbers.
    Is there something, apart from the common gas saving tips, that may be causing a bad mpg?

    Thank you in advance!

  15. #269
    Registered User peekeesh's Avatar
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    Pepezeta, stop and go traffic in the city definitely makes your mpg worse. I mostly drive in the city as well and i get the same mpg as you.

    Sent from my C6806 using Tapatalk

  16. #270
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    City driving will absolutely kill your mileage especially stop and go. Highway if you keep easy on the throttle around 65 mph you'll see around 26 or 27

    Sent from my SCH-I545 using Tapatalk

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